fix(frontend): channel posts show no sender id, a post sent as a chat shows its title and avatar

frontend/src/lib/components/MessageList.svelte

@@ -14,6 +14,8 @@
   import { formatDay } from "#lib/format/datetime.js";
   import { t } from "#lib/i18n/locale.svelte.js";
   import { accounts } from "#lib/stores/accounts.svelte.js";
+  import { chats } from "#lib/stores/chats.svelte.js";
+  import { discover } from "#lib/stores/discover.svelte.js";
   import { events } from "#lib/stores/events.svelte.js";
   import { peers } from "#lib/stores/peers.svelte.js";
   import { toasts } from "#lib/stores/toasts.svelte.js";
@@ -54,7 +56,11 @@
   let highlightTimer: ReturnType<typeof setTimeout> | null = null;
 
   const ownId = $derived(accounts.selected?.tg_user_id ?? null);
-  const isGroupChat = $derived(chatId < 0);
+  const isChannel = $derived(
+    Boolean(chats.byId(chatId)?.is_broadcast) ||
+      discover.get(chatId)?.kind === "channel"
+  );
+  const isGroupChat = $derived(chatId < 0 && !isChannel);
 
   interface Row {
     dayKey: string;